1. Technical Field
The present invention relates to a semicarbazide derivative and a coating composition containing the same and a polycarbonyl compound. More particularly, the present invention is concerned with a semicarbazide derivative or a terminal-blocked form thereof, which is obtained by reacting a polyisocyanate having from 3 to 20 isocyanate groups in a molecule thereof with hydrazine or a derivative thereof, or a mixture of non-terminal-blocked and terminal-blocked forms of hydrazine or a derivative thereof. The present invention is also concerned with a coating composition comprising at least one member selected from the semicarbazide derivative and a terminal-blocked form thereof as a curing agent, and a polycarbonyl compound. Further, the present invention is also concerned with a composition comprising at least one member selected from the semi-carbazide derivative and a terminal-blocked form thereof and at least one member selected from a hydrophilic group-containing compound and a terminal-blocked form thereof (this composition is hereinafter frequently referred to as "semicarbazide composition"), and further concerned with a coating composition comprising this semicarbazide composition and a polycarbonyl compound.
The coating composition of the present invention has not only excellent cold-curing ability and storage stability, but is also capable of forming a coating which has excellent properties, such as excellent water resistance, stain resistance, hardness, toughness, weatherability, dispersion characteristics of pigment, gloss retentivity, adhesion properties, rust preventive properties, water impermeability, heat resistance and chemical resistance, and which is extremely excellent especially in water resistance, stain resistance and hardness. Therefore, the coating composition of the present invention can be advantageously used as a paint, an undercoating or finish coating material for building materials, an adhesive, a pressure-sensitive adhesive, a processing agent for papers, or a finish coating material for textile fabrics.
2. Prior Art
In recent years, in the field of coatings, an aqueous emulsion has been drawing attention as a substitute material useful in the shift from organic-solvent type coating materials to aqueous-solvent type coating materials. However, coatings formed from conventional aqueous emulsion type coating materials are unsatisfactory in respect of various properties, such as water resistance, stain resistance and hardness, as compared to coatings formed from organic-solvent type coating materials.
In an attempt to improve the above-mentioned properties of coatings formed from aqueous emulsion type coating materials, it has generally been conventional practiced to introduce a functional group into an aqueous emulsion type coating material so that a coating comprised of a cross-linked polymer (hereinafter frequently referred to as "cross-linked coating") can be formed.
With respect to an aqueous emulsion type coating material which is capable of forming a cross-linked coating, from the viewpoint of ease in coating operation and the like, it has been desired that such a coating material be of a cold-curing, one-pack type such that a coating material comprising a polymer and a curing agent therefor, both dispersed in an aqueous medium can be cured even without heating to form a cured film due to the evaporation of the aqueous medium after the coating. In recent years, as a coating material satisfying the above desire, a hydrazone-crosslinking type aqueous emulsion obtained by the dehydration-condensation reaction between a carbonyl group and a hydrazide group has been attracting attention.
For example, in Examined Japanese Patent Application Publication No. 46-20053, Unexamined Japanese Patent Application Laid-Open Specification No. 57-3850, Unexamined Japanese Patent Application Laid-Open Specification No. 57-3857, Unexamined Japanese Patent Application Laid-Open Specification No. 58-96643 and Unexamined Japanese Patent Application Laid-Open Specification No. 4-249587, it is proposed to add a dicarboxylic acid bishydrazide as a curing agent to an aqueous dispersion of a carbonyl group-containing copolymer, to thereby obtain a coating composition which has not only good cold-curing ability and storage stability, but is also capable of forming a coating which has excellent hardness and stain resistance. However, with respect to this proposal, the above-mentioned dicarboxylic acid bishydrazide used as a curing agent undergoes hydrolysis during the storage of the coating composition containing the same, so that the cross-linking ability (i.e., curing ability) of the coating composition is lowered with the lapse of time and, hence, the ability of the coating composition to form a coating having good hardness, stain resistance, solvent resistance and the like is lowered with time. In addition, this proposal has a problem in that, because of the use of a dicarboxylic acid bishydrazide (such as adipic acid bishydrazide) having a low compatibility with a carbonyl group-containing copolymer and having a high hydrophilicity, the obtained cross-linked coating is inevitably caused to have extremely poor water resistance.
As can be seen from the above, aqueous coating compositions containing a conventional curing agent and a carbonyl compound become lowered in curing properties with time, so that when such a coating composition is applied to the surface of a substrate, the composition cannot exhibit a satisfactory curing ability. Further, since a conventional coating composition employs, as a curing agent, a dicarboxylic acid bishydrazide having a low compatibility with a polycarbonyl compound, the conventional coating composition has problems in that a cross-linked coating formed therefrom has extremely low water resistance. Therefore, it has been desired to develop an aqueous coating composition which has not only an excellent cold-curing ability and storage stability, but is also capable of forming a coating which has excellent properties, particularly excellent water resistance, stain resistance and hardness.